The present invention relates to a video signal processor, more particularly to a control circuit for controlling a trapping circuit, which is employed in the luminous signal processing system of at least one of the recording and reproducing systems of a home video tape recorder (VTR) so as to remove down-converted color signal components from a low-frequency carrier wave FM signal.
FIGS. 11 and 12 shows parts of conventional recording and reproduction systems, respectively, which are incorporated in the video signal processing IC (integrated circuit) of a home VTR that records or reproduces television video signals of an NTSC system.
In the recording system shown in FIG. 11, the luminous signal (3.58 MHz) components separated from a video signal by means of a comb filter (not shown) are extracted from a video signal by means of the LPF of the luminous signal processing system. The extracted luminous signal components are supplied to an FM modulating circuit 82, by which they are converted into a low-frequency carrier wave FM signal. This low-frequency carrier wave FM signal is supplied to a color signal trapping circuit 83 so as to eliminate the band components of a down-converted color signal.
The output signal (low-frequency carrier wave signal) of the color signal trapping circuit and the output signal (the down-converted color signal) of the LPF 86 are added together into a composite signal, and this composite signal is recorded in videotape. At the time, the composite signal is recorded alternately in the adjacent two video tracks of the video tape by two video heads (not shown) provided for a rotatable cylinder (not shown).
In the playback system shown in FIG. 12, two playback signals reproduced from the video tape by the two video heads of the rotatable cylinder are amplified by a head amplifier (not shown), and are then alternately selected by a switcher circuit (not shown), thus obtaining a continuous signal. Thereafter, the continuous signal is supplied to the color signal trapping circuit 91 of the luminous signal processing system. The color signal trapping circuit 91 removes the down-converted color signal of 629 kHz from the continuous signal, thus extracting a low-frequency carrier wave FM signal.
The low-frequency carrier wave FM signal, thus extracted, is amplified by an FM signal AGC (automatic gain control) circuit (not shown) until it has a signal level required. In addition, the low-frequency carrier wave FM signal is suppressed in level variation. Thereafter, FM demodulation is performed by an FM demodulation circuit 92, thereby extracting the luminous signal component.
From the luminous signal component, FM signal carrier wave components are removed by use of an LPF 93. In addition, timing adjustment is made with respect to the luminous signal component. To be more specific, the signal transmission time is adjusted with reference to the color signal playback signal. Thereafter, the luminous signal component is supplied to an output amplifying circuit (not shown).
A playback signal output from a switcher circuit (not shown) is supplied to an LPF 94 of the color signal processing system, for the extraction of down-converted color signal components. Extracted down-converted color signal components are supplied to a frequency converting circuit 95. Owing to the frequency conversion performed by this circuit, the down-converted color signal components are converted into color signal components. These color signal components are extracted by a BPF 96.
In the conventional recording and reproducing systems mentioned above, the color signal trapping circuits 83 and 91 restricts the band of luminous signal components, without reference to the level of color signal components. Hence, the bandwidth of luminous signal components inevitably decreases, lowing the resolution.
Although not shown, an ACK (automatic color killer) circuit may be employed in the convention recording system shown in FIG. 11. In this case, the ACK circuit checks whether an input video signal includes a color burst signal, which serves as the phase difference of a color signal. If the color burst signal is not included, the low-frequency carrier wave FM signal output from the FM modulating circuit 82 is supplied directly to the adder circuit 87; it is not made to pass through the color signal trapping circuit 83 (through control). In this manner, the band of the luminous signal components is not restricted.
In the current broadcasting technology, however, the television signals of almost all television broadcasts include color burst signals. Even the television signals representing monochromatic images do include color burst signals. Therefore, even if the through control is performed for the color signal trapping circuit 83 in the ACK circuit, it is not necessarily useful.